Presently, there are many suspension systems manufactured for use with auxiliary axles on trucks and trailers. Such axles are of the type that is alternately drawn up beneath the vehicle at times when the vehicle is lightly loaded so that the wheel sets carried by the axle are not in contact with the ground surface beneath the vehicle. The axles may then be selectively pivoted downward to engage the wheel sets with the ground surface to assist in supporting the vehicle when the vehicle is heavily laden. Virtually all of these suspension systems incorporate a trailing support arm anchored at the leading end to the vehicle frame with the auxiliary axle mounted at the trailing end. The trailing arm is pivotable about the leading end, such that the auxiliary axle may be drawn up beneath the vehicle frame and may be lowered to the surface beneath the vehicle as desired. Typically, the springing support utilized to control the axle of the existing systems has been mounted between the auxiliary axle and the underside of the vehicle frame to support and control the auxiliary axle.
The designs of existing suspension systems are built on the assumption that the surface over which the vehicle will be operating is essentially a smooth surface. The designs assume that the up and down motion of the wheel sets on either end of the auxiliary axle will be generally in unison. Suspension systems of this type are typified by the suspension system claimed in U.S. Pat. No. 4,881,747 to Raidel. The Raidel suspension system functions around two torque tubes that form a parallelogram at the suspension points of each of the pair of wheels. The parallelogram allows for motion only in the vertical plane defined by the parallelogram.
No provision is made in the Raidel design and other designs for the torque that is induced in the suspension system as a result of operating over uneven surfaces, where the rolling motion of the axle causes the wheel set on one end of the axle to be compressed in its full upward position while the wheel set on the other end of the axle is at its fully extended position. This results in the torque being transmitted to the axle suspension system itself and ultimately to the frame of the vehicle. Since there is virtually no compliance designed into the existing systems to accommodate rotational forces induced by the vehicle operating over greatly uneven surfaces, the suspension system and the frame must be substantially strengthened in order to absorb the very substantial torque moments generated by such motion of the heavily laden vehicle. Such strengthening has been by using a double channel frame or increasing the depth of the frame.
Such torques are transmitted as a bending torque and are borne by the suspension components and the frame itself. Over time such torques induce failures in the suspension system and in the frame itself. The existing solutions to alleviate vehicle chassis and suspension component breakage due to torque stress have been simply to make these components heavier and larger. Heavier components only prolong the time until failure occurs and add unneeded weight and additional costs to the vehicle. When breakage due to such torques ultimately does occur, it adds to the maintenance required by the vehicle.
There is a need to achieve more capability for commercial vehicles to operate over uneven and off-road surfaces, such as at construction sites and the like. The auxiliary axles needed to provide this additional load carrying capability over such surfaces should be low cost. Additionally, the design of the axles should minimize the weight of the axles and associated suspension system in order to maximize the payload of the vehicle. A suspension mechanism to absorb the bending torques would meet these objects. To date, no existing suspension which is used in conjunction with a solid beam axle has any mechanical features designed to absorb the torsion that is induced by the uneven raising and lowering of the sets of wheels as a function of operation over uneven surfaces.
Another concern, especially for off-road use, is the height above the ground that the auxiliary axle is able to be retracted to. Current suspensions and recent deeper reinforced truck frames have steadily reduced the available vertical lift for a retracted auxiliary axle. The lift height is important to clear irregular obstacles when a vehicle is driven off of a finished surfaced road. Current auxiliary axle suspension systems exacerbate the problem of vertical lift by interposing the springing means between the frame and the trailing arm. Currently, to achieve proper lift height on a typical on-off highway heavy truck, a chassis frame of no more than eleven inches in vertical height must be utilized. Due to this height restraint of the frame rails and to achieve proper lift, the frame rail most often must be made of heavy double rail or of channel design to resist the twisting that is imposed by the uneven compression and extension of the wheel sets on either end of the auxiliary axle.
In view of the foregoing, it is an objective of the present invention to absorb the torque generated by uneven motion of the wheel sets.
It is a further objective of the present invention to be able to provide a given measure of weight bearing capability while utilizing a lighter weight chassis frame.
It is yet another objective of the present invention to increase the lift height of the auxiliary axle when in the retracted position.
It is a further objective of the present invention to minimize wear and breakage of the frame and auxiliary axle suspension system due to bending and torque transfer as a result of the uneven compression and extension of the wheel sets at either end of the auxiliary axle.